1. Field of the Invention
This invention relates generally to record players, and more particularly is directed to an improved record player in which a reproducing stylus is moved linearly in the radial direction of a record disc when tracking the record groove of the latter.
2. Description of the Prior Art
Most existing record players have a tone arm mounted to swing freely about a vertical axis outside the perimeter of the turntable so that the reproducing stylus of a pickup cartridge mounted at the free end of the tone arm moves in an arcuate path concentric with the swinging axis of the tone arm as the stylus tracks the record groove during reproducing of signals recorded in the latter. The foregoing arrangement has simplicity as an important advantage in that frictional resistance to swinging of the tone arm can be minimized to permit the tracking movement to be effected merely by engagement of the stylus in the spiral record groove of the rotated record disc. However, it has been well recognized that the movement of the stylus in an arcuate path when tracking the record groove is undesireable in that the reaction of the frictional engagement of the stylus with the groove is not consistently directed tangential to the latter, particularly as the stylus moves toward the center of the record disc near the end of a play operation.
Therefore, record players have been developed with so-called linear tracking tone arms in which the pickup or reproducing stylus is intended to move linearly along a radius of the record disc in tracking the groove of the latter as the record disc is rotated on a turntable. However, in the case of a linear tracking tone arm, the engagement of the stylus in the spiral record groove cannot be relied upon to provide a motive force for effecting the actual tracking movement of the tone arm. Thus, in an existing linear tracking tone arm, the latter is mounted on a tone arm support which is moved, as by a rotated feeding screw, in a feeding path that is in parallel, spaced relation to the radius of the turntable along which the pickup stylus is to move. The feeding screw is rotated by means of a servo motor so that the speed of movement of the tone arm support along the rotated feeding screw will approximate the speed of movement of the stylus in the radial direction on the record disc due to the engagement of the stylus with the spiral record groove. Any deviation of the speed of movement of the tone arm support on the rotated feeding screw from the speed of movement of the stylus due to engagement of the latter in the groove of the rotated record disc would cause the stylus to move transversely in respect to the record groove with consequent damage to the stylus or to the record disc. Therefore, the existing linear tracking tone arm is pivotally mounted on the support therefor, with the result that any deviation of the speed of movement of the tone arm support along the rotated feeding screw from the speed of radial movement of the stylus on the record disc is accompanied by angular displacement of the tone arm relative to its support.
In the case of a linear tracking tone arm according to the prior art, angular displacement of the tone arm is detected and a corresponding voltage signal is produced for comparison with a reference voltage to provide a corresponding control signal by which the speed of rotation of the servo motor driving the feeding screw is controlled in the sense to restore the tone arm to its original or predetermined angular relationship to the tone arm support. However, the foregoing control system employing a voltage-comparison cannot achieve the desired high degree of accuracy and requires relatively complex circuit arrangements, such as, the use of a zener diode for generating the reference voltage, in order to compensate for the temperature characteristics of the control system. Furthermore, the described control system cannot be easily provided in the form of integrated circuits and thus cannot take advantage of the cost reductions inherent in such circuits.
In another linear tracking tone arm of the prior art, switch means are mounted adjacent the tone arm so as to be turned ON and OFF in response to angular displacements of the tone arm relative to its support, and the ON and OFF states of the switch means are employed for controlling the operation of the servo motor in the sense to maintain the tone arm in a predetermined angular relationship to the tone arm support. Such arrangement employing switch means for controlling operation of the servo motor is not completely satisfactory in that erroneous operation of the system may result due to chattering of the switch means.